Genre Definition and Recommendation is a feature where I will define a genre and a sub-genre definition and the make some recommendations.
Science Fiction - Definition found on Wikipedia
Science Fiction- is a genre of fiction dealing with imaginary but more or less plausible (or at least non-supernatural) content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities.
Parallel Universe Definition found on Wikipedia
A parallel universe or alternative reality is a hypothetical or (fictional) self-contained separate reality coexisting with one's own. A specific group of parallel universes is called a "multiverse", although this term can also be used to describe the possible parallel universes that constitute reality. While the terms "parallel universe" and "alternative reality" are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term "alternative reality" that implies that the reality is a variant of our own. The term "parallel universe" is more general, without any connotations implying a relationship, or lack of relationship, with our own universe. A universe where the very laws of nature are different – for example, one in which there are no Laws of Motion – would in general count as a parallel universe but not an alternative reality. The correct quantum mechanical definition of parallel universes is "universes that are separated from each other by a single quantum event."
Josie Byrne's life is spiraling out of control. Her parents are divorcing, her boyfriend Nick has grown distant, and her physics teacher has it in for her. When she's betrayed by the two people she trusts most, Josie thinks things can't get worse.
Until she starts having dreams about a girl named Jo. Every night at the same time—3:59 a.m.
Jo's life is everything Josie wants: she's popular, her parents are happily married, and Nick adores her. It all seems real, but they're just dreams, right? Josie thinks so, until she wakes one night to a shadowy image of herself in the bedroom mirror – Jo.
Josie and Jo realize that they are doppelgängers living in parallel universes that overlap every twelve hours at exactly 3:59. Fascinated by Jo's perfect world, Josie jumps at the chance to jump through the portal and switch places for a day.
But Jo’s world is far from perfect. Not only is Nick not Jo's boyfriend, he hates her. Jo's mom is missing, possibly insane. And at night, shadowy creatures feed on human flesh.
By the end of the day, Josie is desperate to return to her own life. But there’s a problem: Jo has sealed the portal, trapping Josie in this dangerous world. Can she figure out a way home before it’s too late?
From master of suspense Gretchen McNeil comes a riveting and deliciously eerie story about the lives we wish we had – and how they just might kill you.
Tandem by Ann Jarzab
Everything repeats.You. Your best friend. Every person you know.Many worlds. Many lives--infinite possibilities.Welcome to the multiverse.Sixteen-year-old Sasha Lawson has only ever known one small, ordinary life. When she was young, she loved her grandfather's stories of parallel worlds inhabited by girls who looked like her but led totally different lives. Sasha never believed such worlds were real--until now, when she finds herself thrust into one against her will.To prevent imminent war, Sasha must slip into the life of an alternate version of herself, a princess who has vanished on the eve of her arranged marriage. If Sasha succeeds in fooling everyone, she will be returned home; if she fails, she'll be trapped in another girl's life forever. As time runs out, Sasha finds herself torn between two worlds, two lives, and two young men vying for her love--one who knows her secret, and one who thinks she's someone she's not.The first book in the Many-Worlds Trilogy, Tandem is a riveting saga of love and betrayal set in parallel universes in which nothing--and no one--is what it seems.